Conventionally, for a flow measuring device that measures an intake air amount, for example, there is known a device that employs a thermal-type measuring method whereby a signal is produced in accordance with a flow rate by use of heat transfer between the device and air. The flow measuring device includes a housing and a sensor described as below. The housing is disposed to project into an intake passage leading to an internal combustion engine, and defines an internal passage which takes in a part of intake air flowing through the intake passage and through which the taken-in air passes. The sensor projects into the internal passage, and produces a signal according to the intake air amount by heat transfer between the sensor and the intake air passing through the internal passage.
The housing is a hollow body made of resin and having a hollow portion, and the hollow portion is used as the internal passage, and the shape of the hollow portion is unsuitable for a simple removal of a metal mold. For this reason, for example, after injection-molding at least two resin parts for forming the hollow portion, the two resin parts are joined together by an adhesive material or the like so as to provide the housing (the resin part for forming the hollow portion is hereinafter referred to as a half hollow body. In the following description, an example of formation of the hollow portion from two half hollow bodies will be explained).
Recently, as a more cost-advantageous mode of joining over joining by an adhesive material, there is proposed a mode in which two half hollow bodies are joined together by injection molding from resin fluid. Specifically, the two half hollow bodies are arranged in metal molds for injection molding, and joining edges of the two half hollow bodies are brought into abutment with each other in the metal molds so as to form a linear space separately from the hollow portion. Then, this linear space is filled up with the injected resin fluid, and the two half hollow bodies are joined together (the linear space filled up with the resin fluid is hereinafter referred to as a filled space).
When the joining by injection molding is employed, on a hollow wall surface that defines the hollow portion, stress is produced in a direction in which the hollow wall surface projects into the hollow portion due to injection pressure. Accordingly, the hollow wall surface is deformed to project by the injection pressure, so that the resin fluid may leak out. As described above, the shape of the hollow portion is unsuitable for a simple removal of a metal mold. Thus, the metal mold cannot be disposed in the hollow portion to prevent the projection of the hollow wall surface, and measures thereby need to be taken separately.
For a method for making the resin hollow body, there may be employed a method referred to as a die slide injection molding (abbreviated as DSI) method having an advantage in terms of cost and quality (see, e.g., JP2013-007705A). In case the DSI method is adopted, the method for making the resin hollow body is divided mainly into, for example, a forming process in which the two half hollow bodies are shaped by injection molding, and a joining process in which the two half hollow bodies are joined together. In the joining process, by relative displacement between the metal molds used in the forming process, without taking out the two half hollow bodies from the metal molds, the hollow wall surface is exposed, and the joining edges of the two half hollow bodies are brought into abutment with each other so as to form the hollow portion and the filled space. Then, the resin fluid is injected into the filled space and the joining edges are joined to each other.
As a result, the half hollow bodies, which have been injection-molded in the forming process, can be joined together promptly in the joining process before warping deformation or the like develops after the forming. Consequently, reduction of production man-hours, improvement of the joining part in quality and so forth can be achieved to ensure an advantage in terms of cost and quality. Therefore, a measure to restrict the projection of the hollow wall surface needs to be taken in order to employ the DSI method as the method for making the resin hollow body.